1. Technical Field
The present invention relates to an apparatus for exposing films, and more particularly, to a printing film exposure method and apparatus using a liquid crystal display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for facilitating the exposure of a film used for printing documents.
2. Related Art
Printing technology, such as offset printing, helps meet the critical need in society to disseminate and preserve knowledge. FIG. 1 is a block diagram showing process steps of an offset printing method. FIG. 2 illustrates an example of a document that may be duplicated by offset printing.
Referring to FIG. 1, the offset printing method includes a drafting step 11S, wherein a document that is to be printed is photographed and drafted for printing; a planning step 12S, wherein the contents of the printed material that is to be produced is decided; and a correcting step 13S, wherein a corrected copy for reproduction is determined by deciding the overall color coordination of the original document based on the results of the planning step 12S. The offset printing method also includes a plate-making step 14S, wherein the plate that transfers the ink to an intermediate printing medium is fabricated; and a printing step 15S, wherein the copy is printed on a final medium using the plate and intermediate printing medium.
The plate-making step 14s will now be described in more detail. Basic colors such as red (R), yellow (Y), and blue (B), and their intensities, are combined to represent all of the colors in the original copy 20. During the plate-making step, the R, Y, and B color concentrations of the original copy 20 are expressed in the plates.
FIG. 2 illustrates the original copy 20 and labels the component colors R, Y, and B. FIGS. 3A to 3C illustrate plan views of a mask for each red color concentration with respect to the original copy 20. For example, as shown in FIG. 2, the original copy 20 is formed of three patterns of the color red (R), each representing a different concentration R1, R2, and R3; one pattern of the color yellow (Y) representing the concentration Y1; and two patterns of the color blue (B), each representing the two different concentrations B1 and B2. As examples, the concentration of R1 may be 10%, the concentration of R2 may be 20%, and the concentration of R3 may be 30%. The masks for each color concentration may be prepared by cutting a pattern into each mask that matches each of the R, Y, and B concentration patterns.
An exemplary process for fabricating masks from white paper for the color red (R) and its three concentrations R1, R2, and R3 will be described. A piece of white paper is selected and cut out along the pattern for R1, thereby forming a first mask M1, as shown in FIG. 3A. Subsequently, another piece of white paper is selected and cut out along the pattern for R2, to form a second mask M2, as shown in FIG. 3B. Finally, a third piece of white paper is selected and cut out along the pattern for R3, thereby forming a third mask M3. A mask for each of the concentrations for the colors yellow (Y) and blue (B), are also fabricated.
Thereafter, concentration plates are prepared for each concentration of the colors red (R), yellow (Y), and blue (B). The number of concentration plates required is equal to the number of the masks formed for the color concentrations. More specifically, the original copy 20 shown in FIG. 2 includes three patterns for the color red (R), one pattern for the color yellow (Y), and two patterns for the color blue (B). Therefore, six concentration plates are required. Each concentration plate corresponds to a color concentration in the original copy 20. Accordingly, the concentration plate corresponding to the first mask M1 has a concentration of 10%, the concentration plate corresponding to the second mask M2 has a concentration of 20%, and the concentration plate corresponding to the third mask M3 has a concentration of 30%. Similarly, the concentration plates corresponding to the masks of the colors of yellow (Y) and blue (B) have concentrations that correspond to the yellow concentration and the blue concentrations in the copy 20.
Subsequently, the prepared masks and concentration plates are used to expose R, Y, and B films to form patterns corresponding to the shapes defined on the masks at the intensities determined by the concentration plates. FIG. 4 illustrates exposing an offset printing film for the red color in the original copy 20. FIGS. 5A to 5C illustrate plan views of R, Y, and B films patterned for reproducing the R, Y, and B colors in the original copy 20.
The first mask M1 having the pattern for R1, the first concentration plate 22a having the R1 concentration of 10%, and the R film 23 for forming the pattern of R1 are aligned over a light-exposing device 30. Then, the light-exposing device 30 illuminates the first mask M1, the first concentration plate 22a, and the R film 23. Accordingly, the light transmitted from the light-exposing device 30 passes through the first mask M1 and the first concentration plate 22a, and illuminates the R film 23 with the appropriate pattern at the appropriate intensity. As a result, the R1 pattern having the 10% concentration of the first concentration plate 22a is formed on the R film 23.
Subsequently, the second mask M2 having the pattern for R2 and the second concentration plate 22b having the R2 concentration of 20% are aligned with the R film 23 that already has the R1 pattern. The light-exposing device 30 illuminates the second mask M2 and concentration plate 22b, thereby forming the R2 pattern having the 20% concentration of the second concentration plate 22b. Finally, the third mask M3 having the pattern for R3 and the third concentration plate 22c having the R3 concentration of 30% are aligned with the R film 23 that already has the R1 and R2 patterns. The light-exposing device 30 illuminates the third mask M3 and concentration plate 22c, thereby completing the R film 23 as shown in FIG. 5A.
Similarly, as shown in FIG. 5B, a Y1 pattern is formed on the Y film 24 to provide the pattern needed for the Y color component of the original copy 20. Furthermore, as shown in FIG. 5C, B1 and B2 patterns are formed on the B film 25 to provide the two patterns needed for the B color component of the original copy 20. Subsequently, an iron or steel alloy plate is prepared for each color by treating each plate with an ammonium type photosensitive liquid. Next, light is projected through each film to illuminate the iron plate or the steel alloy plate, thereby copying the pattern formed on the films 23, 24, and 25 onto plates for reproducing the red, yellow, and blue colors. Thereafter, the plates are inserted in the printing apparatus for transferring red, yellow, and blue ink to an intermediate medium, and ultimately to a final medium that bears the reproduction of the original copy 20.
The conventional technique for forming offset printing films has many disadvantages. For example, many masks and concentration plates are required, including one for each concentration of each color. Therefore, reproducing an original copy often requires many masks and concentration plates. As a result, a large amount of time is consumed to fabricate the masks and concentration plates in order to fabricate films. In addition, when a misalignment of the masks occurs causing a misrepresentation of even a single color concentration of the film, the step of fabricating the printing pattern on the film must be restarted from the beginning.